A conventional lumped constant type electromagnetic delay line typically comprises an inductive device consisting of a plurality of turns of electroconductive wire, and chip capacitors connected to a plurality of taps provided in the inductive device so as to form a ladder circuit consisting of a plurality of sections. The inventor of this patent application previously proposed in U.S. Pat. No. 4,649,356 an electromagnetic delay line of this type featuring a small size and low manufacturing cost.
According to this electromagnetic delay line, as illustrated in FIG. 7, a pair of first intermediate electrodes 3 and 5 serving as input and output electrodes and second intermediate electrodes 7 placed between the first intermediate electrodes 3 and 5 are all mounted on a major surface of a rectangular mounting plate 1 in mutually spaced relationship, and an inductive device 11 is formed by a plurality of turns of electroconductive wire wound around a bobbin 9 consisting of a rectangular plate. Two ends 11a and 11b and intermediate taps 11c of the inductive device 11 are soldered to the first intermediate electrodes 3 and 5 and the second intermediate electrodes 7, respectively, along a long side of the rectangular mounting plate 1, and a composite capacitor 13 consisting of an array of capacitors is soldered to the intermediate electrodes 3, 5 and 7 on the major surface of the mounting plate 1.
The intermediate electrodes 3, 5 and 7 extend from the mentioned long side to the vicinity of the other long side of the mounting plate 1 on which a connecting electrode 15 is centrally formed. The composite capacitor 13 is connected to this connecting electrode 15 via a connecting piece 17, and input, output and common terminals 19, 21 and 23 are connected to the input, output and connecting electrodes 3, 5 and 15, respectively.
As illustrated in FIG. 8, the composite capacitor 13 is provided with an elongated rectangular dielectric plate 13a, a common electrode 13b placed on one side (reverse side as seen in FIG. 8) thereof substantially over an entire length thereof, and a plurality of capacitive electrodes 13c arranged on the other side of the dielectric plate 13a so as to correspond to the first intermediate electrodes 3 and 5 and the second electrode 7. By soldering these capacitive electrodes 13c to the corresponding first and second intermediate electrodes 3, 5 and 7, a lumped constant type electromagnetic delay line is formed.
The inductive device 11 is fabricated as illustrated in FIG. 9 from the view point of improving the production efficiency and reducing the manufacturing cost.
More specifically, an end of electroconductive wire is retained by a clamp of a winding machine as a leader (the right end in FIG. 9), and the wire is wound around the bobbin 25 from right to the left. At an end of each coil section, the wire is pulled out away from the bobbin 25. The wire is then bent back, and the two runs of the wire are twisted with each other. Thereafter, the next coil section is wound in a similar manner following a few turns of wire in a coarse pitch wound around the bobbin 9 as a connecting coil 27. A plurality of such coil sections are thus wound in series, and a part of the wire between each coil section and the next connecting coil (the parts denoted by "x" in FIG. 9) is severed so as to form each inductive device 11 having two ends 11a and 11b.
In FIG. 9, the wire of only the inductive device on the rightmost end is severed, but the remaining inductive devices may be similarly severed and separated.
After each coil segment is separated, two coil ends 11a and 11b thereof are bent in parallel with the taps 11c, and soldered to the first intermediate electrodes 3 and 5 while the taps 11c are soldered to the second intermediate electrodes 7. Then, the bobbin 25 is cut off from the remaining part.
By thus forming the inductive devices in series along a long bobbin 9 so as to form taps 11c at a pitch corresponding to the pitch of the first intermediate electrodes 3 and 5, and the second intermediate electrodes 7, the process of fabricating the inductive device as well as the process of assembling the electromagnetic delay line is simplified.
However, there is an ever growing demand for improved cost efficiency, and the Inventor realized that there may be a room for further improvement on the manufacturing cost and the manufacturing efficiency of electromagnetic delay lines.
According to the above described inductive device, it is desirable to be able to solder the taps and the two ends to the corresponding electrodes all at the same time instead of soldering them one at a time in view of the manufacturing efficiency.
However, in reality, because each of the two ends 11a and 11b of each inductive device consists of a single wire, and can therefore easily bend, it is somewhat difficult to place them in proper position along with the taps to solder them to the corresponding electrodes all at the same time. Even when they are placed properly over the corresponding electrodes, a soldering iron often pushes the wire away from the proper position during the process of soldering.
In particular, when electromagnetic delay lines are to be manufactured by using inductive devices which are formed by winding a continuous coil around a rod-shaped bobbin 25 and separating it into individual inductive devices, even though a high production efficiency can be attained for the production of inductive devices, there still is a room for improvement in the process of assembling them into electromagnetic delay lines because, due to the above mentioned problem, after the taps each consisting of twisted wire pair are simultaneously soldered to the corresponding electrodes, the two ends must be individually positioned by using a pair of pincers and soldered to the corresponding electrodes.